Carbureting system



y 12, 1959 G. BURRELL 2,886,021

CARBURETING SYSTEM Filed Nov. 2, 1956 2 Sheets-Sheet 1 IN V EN TOR.

Pump

A T TORNEY 2 Sheets-Sheet 2 Filed Nov. 2, 1956 INVENTOR. @Yez/flzzwd/ A TTORNEY quired.

United States Patent CARBURETING SYSTEM M Gilbert Burrell, Lansing, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of,

Delaware a Application November 2, 1956, Serial No. 620,099

12'Claims. (Cl. 123-127) to be relatively uneconomical during normal operation and which latter operationiconstitutes the greatest proportion of operating time of an engine. c c

i As is well known in the carburetion field, it is desirable to have large, referring to flow capacity,induction passages permitting large quantities of air to flow through the engine under high speed or highpower operation and on the other hand to have relatively small induction passages for economicallow speed or low power operation. Accordingly, present practice is to compound carburetors in such a way that a single large carburetor is used which employs a plurality of induction passages in which some or all thereof may be utilized depending on the amount of power required. A carburetor of this general type is shown in copending application Serial No. 264,136 Olson et al., filed December 29, 1951 now Patent No. 2,771,282, issued Nov. 20,1956. In this type. of carburetor primary throttles begin to open first,yunder normal accelerator pedal loading, thereafter followed by the gradual sequential opening of secondary throttles.

With such an arrangement both primary and secondary throttles are functioning over a considerable range of engine operating conditions including some in whichade-j quate power could be furnished more economically through the primary throttlesalone. A somewhat similar system employing an air flow responsive valve in the secondary induction passage is shown in Patent 2,434,192 Braun. Other etforts have been made to compound carburetors in which the secondary or auxiliary throttles are gradually brought into operation by power actuating means as may be typified by the patent ;to Brau n 2,705,942.

The present invention represents an improved and simplified compound carburetor system in which a plu rality of relatively small carburetors is utilized in such a way that the engine operates on only one of the carburetors during normal operation with the additional carburetors being utilizedonly to provide highengine power requirements and further in which there is no modulation of the throttles of the secondary or auxiliary carburetors. The presentdeviceprovides a unique control system whereby the normal operating or master car-J buretor is manually controlled and in turn determines when the additional carburetors willbe rendered operative to supplement the supply of combustible mixture and thereby increase the power output ,of the engine. While 2,886,021 Patented May 12, 1959 power force to actuate the auxiliary throttles when oper-, ating conditions so require. The auxiliary throttle power;

actuating device and the, manual throttle means for controlling the device are arranged to insure that the auxiliary throttles are either opened or closed without thewintermediate positioning or modulation which has been co ns mon in the past.

The present carbureting system will hereinafter badescribed in detail.

In the drawings:;

tern;

Figure 3 e is Figure 1; c

Figure 4 isan enlarged fragmentary view showing the servo controlling air switch; and l a a Figure 5 is a view alongline 5--5of Figure 4.-

The exact number of carburetors which maybe compounded according to the teaching of the present device is not so limited but for the sake of illustration, and,

further as being representative of a systemwhich has actually been built and performs very satisfactorily, the

present invention will be shown as utilizing three twobarrel carburetors indicated generally at 10, 12 and, 14.1

A manifold developed for use with the illustratediin-l stallation is shown and described in copending applica-.:

tion B25,698 Burrell. l

Except as will be hereinafter specifically pointed out the carburetors are of the same basic construction although the auxiliary carburetors ,12 and 14 have been modified to eliminate unnecessary components such as choke valves, either manual or automatic.

to supply air in an amount determined by engine and operator demand. The manualflcarburetor includes a, throttle shaft 20 on which a pair of throttle blades 22 are fixed for rotation. Also fixed on shaft 20 exteriorly of the carburetor body is a lever 24 to which the accelerator control pedal linkage, not shown, is articulated at 26. The lever 24 is rotated in a clockwise direction, as viewed in Figure 2, to open the throttles 22. The normal fastand slow idle adjustments 28 and 30 are provided in order to insure proper engine operating speeds.

return check 32-is provided to prevent the throttle from, closing too rapidly to avoid the possibility of the engine, stalling when the power demands thereon are suddenly A throttle released.

3 The, auxiliary carburetors 12 and 14 respectively in clude shafts 34 and 36 upon which are mounted throttle blades 38 and 40. :As viewed in Figure lthrottle shaft 34 extends through carburetor 12 terminating ,exteriorly thereof and having a lever 42 fixed for rotation therewith. Articulated to lever 42 isone end of a control rod 44;the:

other end, of which is similarly articulated to a lever, 46

fixed to throttleshaft 36 oncarburetor 14. In this way as shaft 34 is rotated to open the auxiliarythrottle valves 38 the sameopening movement will be trans- Figure 1 is a plan view of the, presentcarbure ti ng sys-,

Figure 2 is an elevational View of the subject system; a fragmentary view along line 3-3 ,of,

mitted through the control rod 44 to lever 46 providing unison operation of the auxiliary throttle valves 38 and 40.

In order to eliminate the use of choke valves in the auxiliary carburetors 12 and 14 a latching device is provided which will insure that the auxiliary throttle valves 38 and 40 cannot'be opened 'until such time as the engine has warmed sufiiciently to'permit their use without undue leaning of the combustible charge. To provide this operation, a' lever is fixed for rotation with the choke shaft 52 of carburetor 10. One end of a rod 54 is articulated to lever 50 at 56 and the other end of the rod articulated to an arm 58 of a lever 60 suitably pivoted at 62 to the casing'of carburetor 12. A lever 64 is fixed to auxiliary throttle shaft 34 and includes a tang or projection 66 which is adapted to coact with an arm 68 oflever'60 in such a way that when the engine is cold the parts will be in the position shown in Figure 2 and the lever 64, and hence the throttle valves 33, will be latched in a closed position preventing their opening irrespective of the degree of opening of the manual throttles 22. Inasmuch as the auxiliary'throttle valves 38 and 40 are coupled together, as described above, it is apparent that the thermostatic latching means, as just described, will also prevent the premature operation of auxiliary throttles 40. As the choke valve.18v is opened with increasing engine temperatures, lever 50 will be rotated in a counterclockwise direction causing clockwise movementof lever 60 permitting throttles 38 and 40 to be opened when such operation is indicated by the controlmechanism to be hereinafter described.

Before passing on to the description of the auxiliary throttle control mechanism, it should be noted that the auxiliary carburetors 12- and 14 include main fuel supply systems similar to the main fuel supply system of the manual carburetor 10 including accelerator pumps, not shown, 'butwhich pumps are actuated by throttle rods 70, 72 and 74; respectively articulated to. throttle levers 24, 64 and 76. The auxiliary carburetors do not include idling fuel systems and the throttle valves 38 and 40 are intended to be completely closed during idling conditions. To insure that the auxiliary throttle valves will becompletely closed for most effective idling operation, auxiliary springs 78 and 80 are respectively fixed at one end to levers 42' and 46 and anchored at the other ends to the associated carburetor casings through studs 82 and 84 to impart a relatively strong closing bias to these valves. While not shown in the drawings, the accelerator pumps of carburetors 12 and 14 also include return springs which are operatively connected to throttles38 and 40 but on the opposite transverse sides of the carburetors relative to springs 78 and 80. The accelerator pump springs exert a' closing force on the auxiliary throttles like springs 73 and 80' and by disposing these similarly acting spring forces on opposite sides of the carburetors a substantially uniform or transversely balanced closing moment is applied to the auxiliary throttles to insure complete closing against the induction passage walls.

In View of the relatively heavy closing moment. imparted to the auxiliary throttle valves by. the accelerator pump springs and auxiliary springs 78 and 81}, it is desirable to use 15, rather than the normal 10", throttles and further tomake these throttles relatively, thick. In these waysthe possibility of the auxiliary throttles sticking in a closed position against the induction passage walls is considerably reduced. In view of the desirability of having' the idling mixture supplied only through the manual or master carburetor 10 and therefore the provision of theunusually largeclosing-force applied to the auxiliary throttles, as described, it is apparent that if means were not provided for actuating the auxiliary throttles automatically, that is, by providing a power force for actuation, the accelerator pedal resistance against which the operators foot. would be required to act in order to open theauxiliary-throttles .wouldbe considerable to the extent of being annoying if notfatiguingto the operator. par- 4 ticularly under conditions where high power operation had to be resorted to frequently.

To obviate the necessity for manual operation of the auxiliary throttles a unique auxiliary throttle control system has been developed and will now be described. As already indicated, normal engine operation, i.e., all operation except that requiring relatively high horsepower output, is achieved through the combustible mixture variably supplied by the manual carburetor 10. Further, no demand is made on auxiliary carburetors 12 and 14 until the master carburetor 10 is substantially open. Thus the vehicle may be operated at relatively high speeds without recourse being had to the auxiliary carburetors. As a consequence, normal engine operating demands will be satisfied under very economical conditions since only two of the six, in the installation illustrated, induction passages will be functioning. It is only under exceptionally high power demands that the remaining four induction passages will be utilized. While numerous power systems, electrical, hydraulic, etc., may be employed to provide the actual force for opening the auxiliary throttles, under the control of the manual throttle, it has been found most satisfactory to utilize a vacuum force which is readily available in the engine and the operating components of which vacuum system are relatively inexpensive for the actuating power produced. This is particularly true in contrast to an electrical system, which might also be utilized, but which would require a rather large and hence expensive solenoid device.

In one type of engine with which the present carbureting system may be used, a vacuum booster pump is provided which maintains vacuum at a relatively constant level for various uses, e.g., windshield wiper actuation. This same source of vacuum is utilized in the present system to provide the force for opening the auxiliary throttles. A vacuum servo 92 is mounted on carburetor 12 through a suitable bracket 94. The servo includes a flexible diaphragm 96 to which is centrally secured a rigid operating member 98 articulated at the other end to a rod 100. The other end of rod 100 is articulated to throttle lever 64 in such a way that movement of the diaphragm 96 to the left will affect an opening movement of the throttle valves 38 and, through the operative connection already described, impart a similar opening movement to the throttle valves 40.

Vacuum is supplied to chamber 62 of servo 92 through a nipple. 104 mounted on the servo casing and to which nipple is connected a vacuum conduit 106, the other end of which conduit communicates with an air switch indicated generally at 110. A vacuum supplying conduit 112 is also connected at one end to the valve and at the other end to the vacuum pump 90 whereby a substantially constant value vacuum force is provided at the valve 110 and which vacuum is admitted to servo conduit 106 but only in accordance with the position of the manual throttles22, as will be subsequently considered.

A third. conduit 114 is also connected at one end to valve 110 and at the other end to the induction passage of carburetor 12 anteriorly of the throttle valves 22. The third conduit 114 is provided for admitting atmospheric air to servo chamber 102 when the servo is to be rendered inoperative. The purpose of providing atmospheric air from the induction passage of carburetor 12 is to insurethat clean. air; inasmuch as the air is the induction passage has already passed through the air cleaner, only will be supplied to the servo chamber to prevent the latter from being fouled with impurities.

Referring now to FiguresZ and 4 a lever 116 is fixed to a shaft 118 disposed in carburetor 10. Articulated to an arm 120 of lever 116 is one end of rod 70,the other end of which is similarly articulated to the manual throttle lever 24. Lever 116 includes a pair of arms 12-2 and 12,4: adapted to control the actuation of the air switch 110; The.arms.- 1221-and. 124v are circumferentially spaced 7 insuch a way. that as the manuall throttles are opened the lever 116 will be -rotated in a counterclockwise direction untilarm 122 engages a projection 126 extending from a slidable member 128 of the air switch 110. Arm 122 is positioned so that it will not engage projection 126 until the manual throttles 22 have opened to the point where additional induction passages are necessary to appreciablyincrease the engine power. While the degree of manual throttle opening is obviously not so limited, the present device has been constructed and arranged so that i the manual throttles 22 are substantially three-fourths open before the auxiliary throttles 38 and 40 are opened.

After the manual throttles have opened sufficiently arm 122 engages the projection 126 so that the remaining opening movement of the manual throttles will cause the slide member 128 to be shifted to a position in which the vacuum supply conduit 112 is communicated with the servo supply conduit 106 to admit vacuum to servo 92 and thereby move the diaphragm to open the auxiliary throttles as already described. Upon moving the manual throttles toward closed position the arm 122 will disengage projection 126 permitting a spring biased plunger 130 to return the slide member 128 to the upper positionshown in which the servo supply conduit 106 will be communicated to the conduit 114 admitting atmospheric air to servo chamber 102 permitting springs 78 and 80 as well as the accelerator pump springs, supra, to move the auxiliary throttles to their closed position. I

Considering now further details of air switch 110, the latter includes a casing 132 having relieved portion 134 within which is slidably disposed the member 128. Casing 132 is further relieved at 136 to permit projection 126 on member 128 to extend therethrough. A plurality of ports 138,140 and 142 are formed in casing 132 and respectively communicate at one end to atmospheric conduit 114, servo supply conduit 106, and vacuum supply passage 112. The inner surface of member 128 in abutting relation with easing portion 134 is relieved'to provide a portion 144 which is long enough to uncover and hence communicate any two adjacent ports. In the upper position shown in Figures 4 and 5, ports 138 and 140 are in communication admitting atmospheric pressure to servo chamber 102 under which condition the auxiliary throttles are closed. When member 128 is moved to its lower position by arm 122 of lever 116, supra, port 140 communicates with port 142 admitting vacuum to chamber 102 and opening the auxiliary throttles. Depending on whether member 128 is in its upper or lower position port 142 or 138 is blocked consistent with the operation just described. i

A flat spring 150 is supported at its ends within casing 132 and is adapted to engage a projection 152 formed on member 128 to hold the latter in sliding contact with the casing.

In the event plunger 130 is unable to shift air switch member 128 from the fdown or auxiliary throttle opening position which would cause the operator to lose control of the engine, arm 124 of lever 116 is adapted to engage the underside of projection 126 to force the slide member 128 to its upper or servo venting position.

Inasmuch as the engine operates on the center or manual carburetor alone under all except very high power output conditions, it has been found unnecessary to modulate the auxiliary throttles 38 and 40. Accordingly, the actuation of the auxiliary throttles is such that they are either fully closed or fully opened and there is no dwelling at intermediate positions. This represents a departure from previous carburetors in which efforts have been made to control auxiliary or secondary throttles with'power actuating mechanisms. In most of these latter cases the amount of opening of the secondary or auxiliary throttle has been determined bythe load on the engine, as manifested by the level of manifold vacuum, or engine speed frequently represented by a vacuum signal, the magnitude of which is proportional to the velocity of air flow through the primary or manually controlled throttle. The latter signal sometimes being combined with a modifying vacuum Sig-1 advantages, has in fact proven to be inferior to the unique operfor closed operation of auxiliary throttles as set forth in t e present invention. By designing the present device in such a way as to require supplemental operation of the auxiliary carburetors only during conditions of high horsepower output demand, and further in recognizing the lack of need for auxiliary throttle modulation, a simpler mechanism has been developed in which the power response is faster than in devices heretofore known.

It isapparent that various modifications of the subject system may be made within the scope of the inventive teachings herein contained.

I claim: I

1. A carburetor control system for an internal combustion engine comprising a primary carbureting device having throttlemeans, means for manually actuating said throttle, means for controlling the air fuel mixture in said carburetor, an auxiliary carburetor adapted to supplement the quantity of combustible mixture supplied by said manual carburetor to said engine, said auxiliary carburetor including throttle valve means, power means for controlling said auxiliary throttle valve means, a control device operated by. said manual throttles for controlling the operation of said power means in accordance with the position of said manual throttle means, and means adapted to render said control device inoperative to actuate said auxiliary throttle regardless of the position of the manual throttle means.

2. A carburetor control system for an internal combustion engine comprising a primary carburetingdevice havingthrottle means, means for manually actuating said throttle, means for controlling the air fuel mixture in said carburetor, a plurality of auxiliary carburetors adapted to supplement the quantity of combustible mixture supplied by said manual carburetor to said engine, said auxiliary carburetors including throttle valve means, power means for controlling said auxiliary throttle valve means, a control device operated by said manual throttle for controlling the operation of said power means in accordance with the position of said manual throttle means, and temperature responsive means for latching said auxiliary throttles in a closed position.

3. A carburetor control system for an internal combustion engine comprising a primary carbureting device having throttle means, means for manually actuating said throttle, means for controlling the air fuel mixture in said carburetor, an auxiliary carburetor adapted to supplement the quantity of combustible mixture supplied by said manual carburetor to said engine, said auxiliary carburetor including throttle valve means, spring means for biasing the auxiliary throttle means in a closed position, power meansfor opening said auxiliary throttlevalve means, said power means including a servo operatively connected to said auxiliary throttle means, a switch controlling the actuation of said servo, and means operatively connecting said manually. actuated throttle and said switch whereby during normal operation of said primary carburetor said servo is ineffective to actuate theauxiliary throttle means, said servo being adapted to move said auxiliary throttle means to a full open position whenever the manual throttle actuates said switch indicating a. power need requiring the combined output of the primary and auxil-.

iary carburetors. r 4. An internal combustion engine comprising a plurality of compounded carburetors, each of said carburetors including a throttle valve, means for manually controlling the throttle valve of oneof said carburetors, the remainder of said throttle valves being coupled together for unison operation, power means for controlling the actuation of said coupled throttle valves, a mechanism controlled by said manual throttle valve for actuating said power means, a choke mechanism for controlling the air fuel ratio mixture in the manually operated carburetor, and means connecting said choke mechanism to said coupled throttles to prevent the latter from being opened until the engine temperature reaches a given value.

5. An internal combustion engine comprising a plurality' of compounded carburetors, each of said carburetors including a throttle valve, means for manually operating the throttle valve of one of' said carburetors, means for controlling the actuation of the remaining throttle valve whereby said valve may only be fully opened or fully closed, said controlling means including spring means biasing said remaining throttle valve in a closed position, a servo for opening said remaining valve, a device for controlling the actuation of said servo, a lost motion connection between the manual throttle operating means and said device whereby said manual throttle may be substantially opened before said servo opens said remaining throttle valve, and an engine temperature responsive means for latching the remaining throttle in a closed position.

6. An internal combustion engine comprising a primary carburetor, a secondary carburetor, each of said carburetors including a throttle valve, a lever fixed for rotation with the throttle valve of said secondary carburetor, a vacuum actuated servo articulated to said lever for opening the associated throttle valve, resilient means biasing the secondary throttle valve in a closed position, means for manually actuating the throttle valve of the primary carburetor, an air switch, a first conduit connecting said air switch with said servo, a second conduit connecting said switch with a source of substantially constant value vacuum, a third conduit communicating atmospheric air to said switch, said switch including a member movable to a first position in which said first and third conduits are in communication admitting atmospheric air to said servo means and permitting said spring means to close said secondary throttle, said valve member being movable to a second position in which said first and second conduits are in communication to admit vacuum to said servo to open said secondary throttle, means biasing said switch member in said first position,.and a lost motion connection between said primary throttle valve and the slidable member of said air switch, said lbst motion connection shifting said switch member to its second position after said primary throttle is substantially open.

7. An internal combustion engine comprising a primary carburetor, a secondary carburetor, each of said carburetors including a throttle valve, a lever fixed for rotation with the throttle valve of said secondary carburetor, a vacuum actuated servo articulated to said lever for opening the associated throttle valve, resilient means biasing the secondary throttle valve in a closed position, means for manually actuating the throttle valve of the primary carburetor, an air switch, a first conduit connecting said air switch with said servo, a second conduit connecting said switch with a source of substantially constant value vacuum, a third conduit communicating atmospheric air to said switch, said switch including a member movable to a first position in which said first and third conduits are in communication admitting atmospheric air to said servo means and permitting said spring means to close said secondary throttle, said valve member being movable to a second position in which said first and second conduits are in communication to admit vacuum to said servo to open said secondary throttle, means biasing said switch member in said first position, a lever pivotally mounted on said primary carburetor adjacent said switch, a rod articulated between said.

pivotal lever and the primary throttle valve, said pivotal lever being adapted to engage said valve member when said primary throttle is substantially open whereby additional opening movement of said primary throttle will shift said valve member to its second position.

8. An internal combustion engine comprising a primary carburetor and a plurality of secondary carburetors, each of said carburetors including a shaft upon which a throttle valve is fixed to control the flow of combustible mixture in the associated carburetor, a lever formed on each of said auxiliary throttle shafts, a rod articulated respectively at its ends to said levers whereby said secondary throttles are actuated in unison, spring means fixed to said secondary throttle shaft levers and adapted to bias said secondary throttle valves in a closed position, a vacuum actuated servo device articulated to one of said secondary throttle shafts, an air switch, a first conduit connecting said air switch with said servo, a second conduit connecting said switch with a source of substantially constant value vacuum, a third conduit communicating atmospheric air to said switch, said switch including a member movable to a first position in which said first and third conduits are in communication admitting atmospheric air to said servo means and permitting said spring means to close said secondary throttles, said valve member being movable to a second position in which said first and second conduits are in communication to admit vacuum to said servo to open said secondary throttles, means biasing said primary throttle valve and the switch member in said first position, a lost motion connection between said primary throttle valve and said switch member, said lost motion connection being adapted to shift said switch member to its second position after said primary throttle is substantially open.

9. An internal combustion engine comprising a primary carburetor, a secondary carburetor, each of said carburetors including a throttle valve, a lever fixed for rotation with the throttle valve of said secondary carburetor, a vacuum actuated servo articulated to said lever for opening the associated throttle valve, resilient means biasing the secondary throttle valve in a closed position, means for manually actuating the throttle valve of the primary carburetor, an air switch, a first conduit connecting said air switch with said servo, a second conduit connecting said switch with a source of substantially constant value vacuum, a third conduit communicating atmospheric air to said switch, said switch including a member movable to a first position in which said first and third conduits are in communication admitting atmospheric air to said servo means and permitting said spring means to close said secondary throttle, said valve member being movable to a second position in which said first and second conduits are in communication to admit vacuum to said servo to open said secondary throttle, means biasing said switch member in said first position, a lost motion connection between said primary throttle valve and the slidable member of said air switch, said lost motion connection being adapted to shift said switch member to its second position after said primary throttle is substantially open, means for controlling the mixture ratio in said primary carburetor and an operative connection between said ratio controlling means and the secondary throttle lever whereby said secondary throttle is adapted to be latched in a closed position until the'engine operating temperature reaches a given value.

10. An internal combustion engine comprising a primary carburetor, a secondary carburetor, each of said carburetors including a throttle valve, a lever fixed for rotation with the throttle valve of said secondary carburetor, a vacuum actuated servo articulated to said lever foropening the associated throttle valve, resilient means biasing the secondary throttle valve in a closed position, means for manually actuating the throttle valve of the primary carburetor, an air switch, a first conduit connecting said air switch with said servo, a second conduit connecting said first switch with a source of substantially constant value vacuum, a third conduit communicating atmospheric air to said switch, said switch including a member movable to a first position in which said first and third conduits are in communication admitting atmospheric air to said servo means and permitting said spring means to close said secondary throttle, said valve member being movable to a second position in which said first and second conduits are in communication to admit vacuum to said servo to open said secondary throttle, means biasing said switch member in said first position, and a bifurcated lever pivotally mounted on the primary carburetor, means linking said bifurcated lever and the primary throttle valve, a first arm of the bifurcated lever adapted to engage said movable valve member to shift said member to its first position after the primary throttle is substantially opened, a second arm of the bifurcated lever being adapted to engage and shift said member from its second to its first position in the event the movable member biasing means is unable to do so when the primary throttle moves from the open to the close position.

11. An internal combustion engine comprising a primary carburetor, a secondary carburetor, each of said carburetors including a throttle valve, a lever fixed for rotation with the throttle valve of said secondary carburetor, a vacuum actuated servo articulated to said lever for opening the associated throttle valve, resilient means biasing the secondary throttle valve in a closed position, means for manually actuating the throttle valve of the primary carburetor, an air switch, a first conduit connecting said air switch with said servo, a second conduit connecting said first switch with a source of substantially constant value vacuum, a third conduit communicating atmospheric air to said switch, said switch including a member movable to a first position in which said first and third conduits are in communication admitting atmospheric air to said servo means and permitting said spring means to close said secondary throttle, said valve member being movable to a second position in which said first and second conduits are in communication to admit vacuum to said servo to open said secondary throttle, means biasing said switch member in said first position, a bifurcated lever pivotally mounted onthe primary carburetor, means linking said bifurcated lever and the primary throttle valve, a first arm of the bifurcated lever adapted to engage said movable valve member to shift said member to its first position after the primary throttle is substantially opened, a second arm of the bifurcated lever being adapted to engage and shift said member from its second to its first position in the event the movable member biasing means is unable to do so when the primary throttle moves from the open to the close position, .a choke valve for controlling the mixture ratio in said primary carburetor, and an operative connection between said choke valve and the secondary throttle lever whereby said secondary throttle is adapted to be latched in a closed position until the engine operating temperature reaches a given value.

12. An internal combustion engine as defined in claim 10 in which said air switch includes a casing having three spaced passages formed therein, one end of said passages respectively communicating with the first, second and third conduits, the other ends of said passages terminating in the surface slidably supporting the movable switch member, the adjacent sliding face of said member being relieved to establish communication between any two adjacent ends of said passages, and a projection formed on said member and extending through said casing for engagement by the arms of said bifurcated lever.

References Cited in the file of this patent UNITED STATES PATENTS 2,355,716 Ericson et al. Aug. 15, 1944 2,362,879 Bicknell -r Nov. 14, 1944 2,722,206 Ball Nov. 1, 1955 

